This invention relates to a method and apparatus for controlling a printer and, more particularly, to such a method and apparatus for establishing uniform heat distribution for all of the thermal print heads in such a printer, with minimal thermal interference due to the selective energization of adjacent print heads.
In one type of so-called line printer, a "line" of thermal print heads is divided into successive blocks. Each block is conditioned, sequentially, and the respective print heads included in each conditioned block are selectively energized in response to print-control data signals. Such data signals may be represented as, for example, "print" or "no-print" signals, such as in the form of binary "1"s and "0"s, respectively. Head drivers are coupled to the print heads in each block, these head drivers being responsive to the binary "1"s and "0"s to selectively energize the corresponding print heads in each conditioned block. Thus, the print heads in one block are selectively energized, followed by the print heads in the next adjacent block, followed by the print heads in the next adjacent block, and so on.
If all of the print heads in a block are energized, the heat distribution across such heads may be graphically represented trapezoidal in shape. That is, the temperature of the print heads at opposite ends of the block such as the left-most and right-most print heads, generally will be less than the temperature of the remaining print heads, the latter being substantially the same. This difference in temperature is due to the fact that the heat generated by the opposite end print heads is better dispersed than the heat which is generated in the remaining print heads. That is, a head which is interposed between two other heads will be heated, at least in part, by such two heads. However, a head which is disposed at the end of a block is adjacent only one additional head and, therefore, is heated to a lesser extent by this single head.
Now, if the next-adjacent block is conditioned to be energized, the end print head in this block, which is adjacent one of the end print heads in the preceding block, will be "pre-heated" by that adjacent end head. Hence, the temperature of the end head of this next-following block will be greater because it is contributorily heated by the adjacent end head of the preceding block. It is possible, therefore, that the temperature of this end head of the next-following block will be greater than the temperature of any of the remaining heads therein. This non-uniformity in the heat distribution of the next-following block of print heads may result in a printed indicium that is too dark, thus degrading the quality of the image printed by the printer.